Container refrigeration apparatuses that have been known in the art include a refrigerant circuit performing a refrigeration cycle to cool the air in a container for use, e.g., in marine transportation (see, e.g., Patent Document 1). The container is loaded, for example, with plants such as bananas and avocados. Plants perform respiration by absorbing oxygen in the air and releasing carbon dioxide even after they are harvested. As the plants respire, the plants lose the nourishment and moisture stored in them, resulting in a decrease in freshness of the plants. Thus, the oxygen concentration in the container is preferably lowered not to cause breathing problems.
Patent Document 1 discloses an inside air control system which, using an adsorbent adsorbing a nitrogen component in the air through pressurization, generates nitrogen-enriched air having a higher nitrogen concentration and a lower oxygen concentration than the air does, and supplies the nitrogen-enriched air to the interior of the container, thereby reducing the oxygen concentration of the air in the container to reduce the breathing of the plants and easily keep the plants fresh. This inside air control system sends, using an air pump, the pressurized air to an adsorption column housing the adsorbent therein to perform an adsorption operation in which a nitrogen component is adsorbed to the adsorbent. Then, the inside air control system sucks the air from the adsorption column using the air pump to perform a desorption operation in which the nitrogen component that has been adsorbed to the adsorbent is desorbed. As a result, the nitrogen-enriched air is generated.
This inside air control system may be formed as one unit by housing the components of the inside air control system in a hermetically sealed unit case, and this unit may be attached to an exterior space of the container refrigeration apparatus. Thus, even an existing container, if the unit is retrofitted thereto, can control the oxygen concentration in the interior of the container using the nitrogen mixed gas.